The present disclosure relates to thermal growth management. More particularly, the present disclosure relates to a strut assembly for accommodating thermal growth between cases in a bearing compartment of a gas turbine engine.
Thermal growth in gas turbine engines continues to be a challenging design space especially as modern gas turbine engines operate at ever-increasing pressure ratios and hotter cores to extract any additional thermodynamic cycle efficiency.
One area in gas turbine engines where differential thermal growth manifests itself is where outer housing surfaces of the engine bearing compartment are exposed to hot gas flows, while the inner housing surfaces of the same bearing compartment are at a much lower temperature. In addition, the housing of the bearing compartment is also frequently exposed to transient thermal gradients (and resulting thermal and mechanical stresses) due to engine start-ups and shut-downs as part of the gas turbine engine's operational cycles.
In certain types of gas turbine engines, bearing compartments of the engine include two physically attached annular structures (e.g., inner and outer cases). The outer case is often exposed to a high temperature environment (e.g., 1000° F./538° C.), while the inner case is often cooled to a lower temperature (e.g., 150° F./66° C.). As a result, the thermal expansion of the outer case pulls the inner case radially outward causing deformation of the inner case. This deformation, or “lobing” of the inner case, results in an inability to properly seal the inner case with its corresponding mating surface, which allows air to leak into the bearing compartment thus reducing the delta pressure between the inside and outside of the compartment. This makes preventing oil leakage out of the compartment difficult.